This invention relates to a subscription card for a videotex receiver.
The invention can be used in the transmission and display of information on television receivers for purposes of entertainment, information or education. It can advantageously be applied to the system known as "ANTIOPE" (Numerical Acquisition and Televisualisation of Images Organised into Pages of Script) and to the so-called "TITAN" system (Interactive Teletext Terminal Called by Numbering). It is known that the former is essentially a broadcast videotex system (i.e. unidirectional) by means of which alphanumerical information organised into pages and magazines can be put into television lines and that the second is essentially an interactive videotex system (i.e. two-directional) compatible with the ANTIOPE system and affording access to data bases (general information, directories, etc.) and to interactive services (transactions, messages, education) through the telephone system.
In the ANTIOPE system, the distribution of informtion is effected by a method known as "DIDON" (Distribution of Numerical Data) which is a method of distribution in packets, compatible with the distribution of the television signal.
These systems have already been described in numerous articles or patent applications, notably the ANTIOPE system, a detailed description of which can be found in the following documents, which should be regarded as incorporated in this application:
the article by Y. Guinet entitled: "Etude comparative des systemes de teletexte en radiodiffusion. Quelques avantages de la diffusion des donnees par paquets appliquee au teletexte" which appeared in the U.E.R. Cahier Technique, no. 165, October 1977, pages 242 to 253;
the article by B. Marti and M Mauduit entitled "ANTIOPE, service de teletexte", which appeared in the journal "Radiodiffusion Television", 9th year, no. 40, November-December 1975, 5/5, pages 18 to 23;
the "Specification du Systeme de teletexte ANTIOPE", edited by the Centre Commun d'Etudes de Television et Telecommunications (CCETT);
French patent application no. 75 18319, filed on June 6, 1975 and entitled "Data distribution system";
French patent application no. 76 27212, filed on Sept. 6, 1976 and entitled "System for the numerical transmission and displaying of text on a television screen";
French patent application no. 76 29034, filed on Sept. 22, 1976 and entitled "Improvements to systems for the numerical transmission and displaying of texts on a television screen";
the French application for a certificate of addition no. 77 17625, filed on June 3, 1977 and entitled "Data distribution system".
The advent of services of the ANTIOPE and TITAN types raises the question of their taxation, i.e. the implementation of a system by means of which the audience can be identified and monitored. This question arises more generally with any broadcast service tending to make the broadcasting systems more viable by better use of the resources.
Taxation of the subscription type constitutes a both flexible and durable relationship between a service and its users. Such a method of taxation is particularly justified in broadcasting.
Taxation of the type based on consumption may also be used; this method of taxation is fundamental for "interactive" systems (where there is a dialogue between the subscriber and the information source, as in the case of the TITAN system); however, it is of secondary importance in broadcasting systems (in which information is transmitted in one direction to the subscribers, as with ANTIOPE).
There may be intermediate systems known as "quasi-interactive" systems wherein the content of the distribution source is continuously modified to meet the requirements of the users, which are transmitted via a plublic data network. The advent of new distribution means with a very large capacity, such as satellites, will develop this quasi-interactive mode considerably, thus making it necessary to implement a system for controlling access to the information provided.
The problem of access control raises above all the problems of locking up the information when it is broadcast and unlocking it when it is received. Naturally these problems must be resolved in accordance with the specificity of the teletext system to be controlled. In particular, the method of scrambling the information and restoring the intelligibility of the information should not harm the performance of the system.
The essential elements of a system provided with means for controlling access to the information can briefly be described in order to aid understanding of the present invention. This system is shown in FIG. 1.
First, this system comprises known elements characteristics of the ANTIOPE videotex system, namely an emitting centre 2 and receiving stations 4.
The emitting centre receives information from one or more sources of information 5 and comprises:
means 6 for composing a magazine consisting of pages organised into lines of characters, if such means are not already included in the source of information;
a circuit 10 for memorising the magazine in the form of numerical signals grouped into octets (8 binary elements),
a junction 11 connected to the circuit 10,
a distribution multiplexer 12 for inserting the information in the lines of a television signal, this device using the DIDON procedure referred to above.
Each receiving station comprises:
a circuit 14 for receiving and demodulating said television signal,
a line 16 for processing the video picture signals,
a line 18 for processing numerical signals, this line comprising, in particular a numerical data decoder, and finally
a display means 20.
In this type of system, the numerical signals transmitted are grouped in the form of octets which are subdivided into control octets and data octets. The control octets indicate, in particular, the tops and bottoms of pages and beginnings and ends of lines. The data octets, inserted between the control octets, correspond to characters contained in the lines. All these octets, both control octets and data octets, comprise a heavy binary element which is an odd element. The octets wherein the 6th and 7binary elements are zero are the control octets and play a special part in the system.
The system described in this application further comprises:
(A) in the emitting centre 2;
(a) a generator 22 delivering a numerical signal representing an operating key K, this key changing randomly at predetermined intervals of the order of a few minutes, for example;
(b) automatic locking means 24 comprising:
(i) a comparator 28 with an input connected through the junction 11 to the magazine memorising circuit 10 from which it receives clear octets; this comparator is capable of distinguishing, among these clear octets, those wherein the 7th and 6th binary elements are zero; this comparator has two outputs 31 and 32, the first carrying these octets wherein the 7th and 6th binary elements are zero and is connected to the distribution multiplexer 12 (through a junction 11'), and the second carrying the clear octets d.sub.j wherein the 7th and 6th binary elements are not zero;
(ii) a logic circuit 34 of the OR-exclusive type with two inputs, one of which is connected to the second output 32 of the comparator 28 from which it receives the clear octets d.sub.j wherein the 6th and 7th binary elements are not zero; this logic circuit has an output which carries odd-numbered coded octets D.sub.j, the coded octets then being directed (through junction 11') towards the distribution multiplexer 12;
(c) a generator 26 of encoding octets C.sub.j, controlled by the automatic means 24 from which it receives octets indicating the page numbers and line numbers of the data to be transmitted and the signal corresponding to the operating key K; this generator of octets 26 has an output n1 which delivers, for each data octet d.sub.j of a displayable line, an encoding octet C.sub.j, this octet having an even-numbered 8th binary element and 7th and 6th binary elements of zero, this octet being applied to the second input of the gate 34.
(B) in each receiving station 4:
(d) a circuit 36 delivering a numerical signal representing the operating key K in use in the emitting station,
(e) automatic unlocking means 38 comprising:
(i) a comparator 42 with an input receiving the coded octets; this comparator is adapted to distinguish, among these coded octets, those wherein the 7th and 6th binary elements are zero, this comparator having two outputs 43 and 44, the first carrying these octets wherein the 7th and 6th binary elements are zero, this first output being connected to the display means 20, whilst the second carries the coded octets D.sub.j wherein the 7the and/or 6th binary elements are not zero,
(ii) a logic circuit 46 of the OR -exclusive type with two inputs, one connected to the output 44 of the comparator from which it receives the coded octets D.sub.j, this logic circuit having an output which carries decoded octets d.sub.j which are then directed towards the display means 20,
(f) a generator 26' of decoding octets, controlled by the automatic unlocking means from which it receives the octets indicating the page numbers and line numbers of the data transmitted, and the signal corresponding to the current operating key K; this generator of decoding octets has an output 41' which delivers, for each coded octet received, a decoding octet C.sub.j having a heavy binary element which is forced to zero and 7th and 6th binary elements of zero, these octets being applied to the second input of the gate 46.
Locking and unlocking means of this kind can advantageously be used to solve the problem of taxation referred to hereinbefore. For this purpose it is provided, in addition to the operating key whose function has just been defined, subscribers' keys which are generated randomly by a taxation administration centre. These keys have a relatively long service life (from 1 to 12 months), in relation to that of the operating key (which is of the order of a few minutes).
To illustrate the operation of this double key system, one can take the example of a subscription plan using four types of subscription: 1 month, 3 months, 6 months and one year. In addition to its duration, a subscription is characterised by the month in which it starts. Thus, with a plan of this kind, in a given month and for a given service, there are 22 subscribers' keys liable to be used by the users; a monthly key, three three-monthly keys, six six-monthly keys and twelve yearly keys.
Each month, the taxation administration centre provides each distribution centre with a list of 22 subscribers' keys in use for each service distributed by this centre. In addition, it provides the subscription sales points with another list of 4 keys which are to start in the following month (one month, three months, six months and one year), for each service, with the prices of the subscriptions.
A suitable machine, installed in each sales point, records some of these keys in the form of blocks of subscriptions on holders provided for this purpose (such as, for example, information-bearing cards of the credit-card type). The users of the service then insert these cards in their receivers.
For each paying service, approximately every five minutes a new operating key K is generated at random, by each distribution centre concerned. Thus, during a session of a service (one hour or several hours), there may be several dozen operating keys succeeding one another.
As soon as a distribution centre generates a new operating key K, it calculates, for each subscribers' key in use C.sub.i for this service, a message M.sub.i by means of an algorithm M.sub.i =F.sub.C.sbsb.i (K), in which the keys C.sub.i act as the parameters.
Thus, for a service having the subscription plan indicated above, at any one time there are 22 different message in force. The service life of a message is equal to that of the operating key K and for a given service at any one time there are as many messages as there are current subscribers' keys.
All the messages M.sub.i in force together constitute the access-controlling information associated with the service being broadcast. This access control information is obviously not locked up by the electronic lock.
These means for controlling access to the information are shown in FIG. 1. They comprise:
(A) a subscription administration centre 100, which generates numerical signals corresponding to the subscribers' keys C.sub.i, these keys changing randomly at long intervals of the order of a month and according to plans analogous to that given hereinbefore by way of example;
(B) in the emitting centre:
a circuit 102 for forming messages M.sub.i which receives, from the center 100, the signals corresponding to said subscribers' keys C.sub.i, and, from the generator 22, the signal corresponding to the operating key K. These messages are obtained by means of an algorithm F.sub.C.sbsb.i (K) the parameters of which are provided by the C.sub.i 's. The circuit 102 delivers as many messages M.sub.i as there are subscribers' keys C.sub.i, these messages changing with operating key K. All these messages are organised into a special page 104 known as the access control page. This page is transmitted cyclically by the multiplexer 12 but is not displayable;
(C) in each receiving station:
(i) a subscription holder 106 which contains a memory 108 in which is recorded at least one subscription block representing one of the subscribers' keys C.sub.i,
(j) a circuit 110 for restoring the operating key K, connected on the one hand to the circuit 18 from which it receives a message M.sub.i taken from the access control page and selected by the subscription index and, on the other hand, to the memory 108 of the subscription holder from which it receives the subscribers' key C.sub.i. This circuit 110 develops an algorithm K=G.sub.C.sbsb.i (M.sub.i) for restoring the signal corresponding to the operating key K used in the emitting station;
(D) at least one charging station 112 connected to the subscription administration centre 100 from which it receives the signals corresponding to the different subscribers' keys C.sub.i generated by this centre; each of these stations is adapted to receive temporarily subscription holders and to record one of the subscribers' keys C.sub.i in their memories 108.